1. Field of the Invention
The invention relates to turbine assemblies, and is particularly concerned with controlling the flow of fluid through a multi-stage seal from a chamber defined between a turbine rotor and a stator inner casing to a flowpath through the turbine.
2. Description of the Related Art
A known turbine assembly comprises a turbine rotor and a stator. The turbine rotor comprises a plurality of stages of radially outwardly extending fluid cooled hollow turbine rotor blades. The stator comprises an outer casing which defines at least a portion of the radially outer extremity of a flowpath through the turbine. The outer casing encloses the turbine rotor and turbine rotor blades, and the outer casing comprises a plurality of stages of radially inwardly extending turbine stator vanes. The stator also includes an inner casing which defines at least a portion of the radially inner extremity of the flowpath through the turbine. A chamber is defined between the downstream end of the turbine rotor and the inner casing. Pressurised fluid is supplied to the chamber to apply an axial thrust on the turbine rotor to balance the resultant load on the turbine rotor. A multi-stage seal is provided between the turbine rotor and the inner casing to control the flow of fluid from the chamber into the flow path through the turbine.